I notice this site doesn't have much on the KUK submarine U-30. I have a copy of the Warship International No1 1987 article "The Mystery of the Austro-Hungarian Submarine U-30: Some Facts, observations, speculation" by Ing Rene Greger p81-83

I also have a reply in WI No 4 1987 page 337 by G. F. Thierry whose father was Captain Franz Baron Thierry Commanding officer (KUK) Submarines from 1912-1918.

Grieger: "She comenced her first operational deployment with her departure from Brioni naval base at 1700 on 26 Feb 1917. U-30 returned to Gjenovic naval base at 0900 on 16 march in damaged condition. In addition to construction problems, the submarine had been damaged by depth charges when she unsuccessfully attacked a small Allied convoy in the Ionian Sea. Some conning tower plating was cracked or pulled off, and there also was internal damaged. The boat underwent quick repairs at Gjenovic, but technical assistance available was very limited. Herein lies the first possible cause of the vessel's subsequent loss; defective workmanship."

Thierry "Defective workmanship as cause of the loss of this unit is not plausible because the facilities at Gjenovic were not as limited; futhermore, if a more extensive repair would have been necessary, the submarine would have been ordered to the naval Yard at Pola because there was no hurry to send her on action in a not perfect operational condition.'

wiki has the boat having storm damage.

Grieger "Once repaired, U-30 departed Gjenovis at 1630 on 31 mar 1917 on her second and last deployment. According to operational orders on 23 march the submarine was to operate in the central Mediterranean btween malta and crete. If no shipping traffic was met, the operational area was to be moved sothward, even into the Neutral Zone."

U-30 was never seen again following her depature from Gjenovic.